First off, I own the Ultimate Ears UE-5c, which are IEMs, and while they're very expensive, they offer noise reduction more then the Bose QC2. My dad owns the QC2, so yeah, I'd know. Even with no music playing, I can barely hear someone talking to me when they're sitting next to me. It's insane.
Now, as for the QC2 vs. QC3, if you're set on one of the two, get the QC2. The QC2's are more comfortable, since they're a closed set of cans, opposed to the open QC3's. The slight extra weight is worth it.